This invention pertains to color printing. More particularly, this invention relates to color laser printing systems and to image plane registration for color printing systems.
Color image printing systems are known in the art. One color image printing system comprises an inkjet printer. An inkjet printer prints color images incrementally, with a continuous inkjet printing process, piezoelectric inkjet printing process or bubble-jet printing process. However, these inkjet printing processes provide relatively low-cost printing that is often satisfactory for printing color graphics images, but is not necessarily of high enough quality for certain business applications.
Another color image printing system comprises a color laser, or electrophotographic, printer. Color laser printers generate sufficient text and graphics quality for most business applications. However, color laser printers typically require complex and expensive mechanisms when forming and aligning overlaid color frames. Hence, color laser printers are not sufficiently economical for many applications.
One problem encountered with color laser printers relates to registration of individual color image planes that generate a printed color page. A color image plane is an arrangement either in electronic or optical or other physical form representing a distinctive image in one color. One physical form comprises a single color of toner particles. Typically, three or four distinct color image planes are imaged using one of several known techniques and transferred onto a common piece of paper in order to generate a color image. In some cases, a yellow, a magenta and a cyan color image plane are each imaged and transferred onto a common piece of paper. In other cases, a black, a yellow, a magenta and a cyan color image plane are each imaged and transferred. Irrespective of whether individual color image planes are serially or concurrently transferred onto a piece of paper, registration of individual color image planes is very important.
One type of color image printing system builds up four different colored image planes onto a well-controlled substrate before transferring the generated image onto a piece of paper. One exemplary printing system comprises a Hewlett-Packard Color LaserJet 5, manufactured by Hewlett-Packard Co. of Palo Alto, Calif. Such exemplary printing system builds up a color image onto a page size photoconductor drum. The generated image comprises four distinct colors: yellow, magenta, cyan and black. Four developers are used to produce the four colors, with four distinct photoconductor drum rotations being needed to accumulate the four-color toner images.
Another exemplary printing system comprises a Tektronix Phaser 560, manufactured by Tektronix of Wilsonville, Oreg. Such exemplary printing system builds up a color image onto a page size intermediate transfer medium. However, the use of an intermediate transfer medium adds an additional processing step, which increases cost and complexity. Yet another type of color image printing system comprises a Xerox C55 color laser printer. Such laser printer fixes a sheet of paper onto a drum in order to achieve plane-to-plane registration of successively colored image planes.
Each of the above-mentioned printing systems increases the size of the printer or increases the complexity or cost of the printer. Therefore, there exists a need to provide a reduced cost and complexity technique for achieving a multiple pass color laser printer that realizes improved plane-to-plane registration and is usable with a wide range of media types.
A recirculating type paper drive provides a relatively low cost technique for achieving a multiple pass color laser printer having excellent planeto-plane registration and usable with a wide range of media types. According to one implementation, a four pass color laser printer achieves improved registration for most types of printable paper.
According to one aspect, a paper drive sheet feeder system includes an edge guide, a paper transport mechanism, a paper edge detector, and control circuitry. The edge guide cooperates with the paper transport mechanism to guide the edge of a sheet of paper along a travel path of a peripheral device. The paper transport mechanism is configured to move the sheet of paper along the travel path. The paper edge detector is provided along the travel path to detect the leading edge of the sheet of paper. The control circuitry communicates with the paper transport mechanism and the paper edge detector and is operative to locate the sheet of paper in response to the detected leading edge of the sheet of paper along the travel path to accurately superpose successive image planes during a multiple color image transfer process.
According to another aspect, a printing system is provided for printing multiple colors on a sheet of print media. The printing system includes an electrophotographic print engine and a paper drive sheet feeder system. The electrophotographic print engine includes a photoconductor drum and a transfer roller configured to interact in co-rotation with the drum during transfer of a color image plane from the drum onto a sheet of print media passed therebetween. The paper drive sheet feeder system includes at least one edge guide, a sheet transport mechanism, a sheet edge detector, and control circuitry. The edge guide is configured to guide an edge of the sheet of print media along a travel path about the print engine. The sheet transport mechanism is configured to move the sheet of print media along the travel path. The sheet edge detector is provided along the travel path to detect the leading edge of the sheet of print media. The control circuitry communicates with the sheet transport mechanism and the sheet edge detector and is operative to locate the sheet of print media in response to the detected leading edge of the sheet of print media along the travel path to accurately superpose successive image planes during a multiple color image transfer process.
According to yet another aspect, a method is provided for aligning and positioning a sheet of print media to receive multiple, successive color image planes. The method includes: moving a sheet of print media along a travel path; while moving the sheet of print media along the travel path, accurately guiding the sheet of print media along an edge guide to prevent movement in a lateral direction; detecting the leading edge of the sheet of print media to accurately locate positioning of the sheet of print media along the travel path; while moving the accurately located sheet of print media, transferring a first color image onto the sheet of print media; moving and accurately guiding the sheet of print media along the travel path along the guide and about a print engine; following transferring the first color image and moving the sheet, detecting the leading edge of the sheet of print media to accurately locate positioning of the sheet of print media along the travel path; and while moving the accurately located sheet of print media, transferring a second color image onto the sheet of print media accurately aligned atop the first color image.
One advantage is provided by precisely transferring a sheet of print media between successive passes against a photoconductor drum while transferring successive color image planes onto the sheet of print media so as to ensure precise registration between successive color image planes when forming an image.
Other features and advantages of the invention will become apparent to those of ordinary skill in the art upon review of the following detailed description, claims, and drawings.